1. Field of the Invention
The present invention is generally concerned with torsional damper devices comprising at least two coaxial parts mounted to rotate relative to one another within a defined range of relative angular movement against circumferentially acting elastic means.
2. Description of the Prior Art
As is known, this type of torsional damper device is normally incorporated in the design of a friction clutch, particularly for automotive vehicles, for example, in which case one coaxial part comprises a friction disk designed to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automotive vehicle, constituting a part referred to hereinafter for convenience as the driving part, whereas the other of said coaxial parts is carried on a hub designed to rotate with a second shaft, in practice a driven shaft and the gearbox input shaft in the case of an automotive vehicle, constituting a part referred to hereinafter for convenience as the driven part.
This type of torsional damper device is used to permit regulated transmission of rotational torque applied to one of its coaxial parts where the other is itself subject to a rotational torque, in other words, to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the axles in the case of an automotive vehicle.
More often than not, the elastic means disposed in the circumferential direction between the driving part and the driven part comprise a plurality of elastic members extending in a substantially tangential direction relative to a circumference of the damper and all partially housed in an opening formed for this purpose in the driving part and partially housed in an opening also formed for this purpose in the driven part.
Also more often than not, the elastic members utilized are helical springs.
It has previously been proposed to substitute blocks of elastic material for all or some of these springs, however.
Be this as it may, it is common practice to divide the elastic members constituting said elastic means into at least two separate groups and to delay the action of at least one of these groups during relative angular movement between the driving and driven parts, in order to modulate the stiffness of the elastic means operative between the driving and driven parts according to the extent of relative angular movement between them and thus to improve the adaptation of the damper to the specific filtering effect required.
To this end, whereas, in the rest configuration of the damper, all elastic members used are usually disposed without circumferential clearance in the corresponding openings in the driving part, those whose action is to be delayed are, in this rest configuration, disposed with circumferential clearance in the corresponding openings in the driven part, so that they are operative only from the time at which, by virtue of the relative angular movement between the driving and driven parts, this circumferential clearance is absorbed.
However, the stiffness of the elastic means utilized then increases sharply by virtue of the intervention of the second group of elastic members. There sometimes results, when the accelerator pedal of the vehicle is pressed, at least in some specific embodiments, the generation of a noise commonly referred to as a "clunk", whether in motion or stopped. Also, on reversal of the torque between the driving part and the driven part, due to momentary releasing of the accelerator pedal of the vehicle, for example, whether in motion or stopped, there sometimes develops an oscillation phenomenon, the driving part being then subject to very fast retrograde movement followed possibly by it bouncing off the driven part, due to the relatively low stiffness of the first group of elastic members, being the only ones operative at this time.
The noise and oscillation are observed whether the elastic members utilized are springs or blocks of elastic material.
A general objective of the present invention is to provide an arrangement which may be used to reduce or eliminate this noise and oscillation, by ensuring a more progressive changeover from the stiffness of the elastic means disposed between the driving and driven parts when only the first group of elastic members constitutes same and the stiffness of the latter when the second group of elastic members acts in addition to the first.